1. Field of the Invention
This invention relates to soft magnetic materials and more particularly, to compositionally modulated, nitrided alloy films which exhibit a small coercive force, Hc, and are thus suitable for use as magnetic heads. The invention also relates to a method for making such alloy films.
2. Description of the Prior Art
As is well known in the art, existing magnetic heads are usually made of Sendust alloys mainly composed of Fe-Si-Al, amorphous alloys such as Co-Nb-Zr, or ferrites which are small in high frequency loss. In recent years, there is a great tendency toward high density recording of information, for which recording mediums are now being switched over to those mediums having a higher coercive force than conventional mediums. This, in turn, requires soft magnetic materials which have a higher saturation magnetization, 4.pi.Ms. In addition, magnetic materials for the magnetic head are generally required to have good corrosion and wear resistances as well as the high saturation magnetization. Although ferrites have good corrosion and wear resistances, the saturation magnetization is unsatisfactorily as low as 5000 to 6000 G. Amorphous alloys have good magnetic characteristics but are so poor in heat resistance that they are crystallized at high temperatures, resulting in deterioration of the characteristic properties. Currently available amorphous alloys which can withstand a magnetic head gap bonding process are those alloys whose saturation magnetization is, at most, about 10,000 G. Sendust alloys exhibit a saturation magnetization of about 12,000 G but are poor in corrosion resistance. In order to improve the corrosion resistance, Cr or other metals have to be added to the alloy, thus making it practically difficult to provide an alloy whose saturation magnetization is over 10,000 G. The Sendust alloy to which Cr or the like is added is rather poor in wear resistance.
Recently, attention has been drawn to Fe-Si alloys having high saturation magnetization. However, the Fe-Si alloys do no exhibit excellent soft magnetic characteristics as is different from Fe-Si-Al alloys and Co-Nb-Zr amorphous alloys and are poorer in corrosion and wear resistances. Hence, the alloys cannot be used as a magnetic head core.
Attempts have been made to improve the corrosion resistance of the Fe-Si alloy by incorporation of additives. Typical examples of such alloys include Fe-Si-Ru alloys as described in the Bulletin of the Scientific Lecture of The 8th Meeting of the Japanese Applied Magnetic Society, November, 1984. Although the corrosion resistance of the Fe-Si alloys may be improved to some extent by the addition of such elements, the soft magnetic characteristics are not improved at all with an attendant problem that the use of the additive elements in large amounts results in the reduction of saturation magnetization and the deterioration of soft magnetic characteristics.
In order to obtain magnetic alloys which have good soft magnetic characteristics and good resistances to corrosion and wear, various nitrided alloys have been studied including nitrides of Fe as described in J. Appl. Phys. 53(11) P. 8332 (1982) and nitrides of Fe-B alloys as described in Japanese Laid-open Patent Application Nos. 54-94428 and 60-152651. However, the nitriding will impede soft magnetic characteristics. In particular, these alloys present the problem that a coercive force, Hc, which is an index of soft magnetic characteristics, becomes very large.